Under cold start conditions, an engine has cooled to ambient conditions, which may be relatively hot or cold, and each component of the engine warms-up to a desired operating temperature. During this time, emissions may be higher and there may be energy losses such as viscous energy losses due to a relatively cool temperature of fluids (e.g., engine oil, transmission fluid, etc.) circulating through the powertrain.
Some methods for expediting engine heating include exhaust heat recovery. In some examples, exhaust heat is transferred to engine coolant, for example, via a heat exchanger. Such a method, however, may be only marginally effective in quickly heating the combustion chamber and/or reducing fluid viscosity.
The inventors herein have recognized the above problems and have devised an approach to at least partially address them. Thus, a method for heating an engine in a vehicle is disclosed. The method comprises heating intake air via a gas-to-gas heat exchanger, the gas-to-gas heat exchanger in communication with exhaust gases, and heating a fluid which flows through the engine with the intake air via a gas-to-liquid heat exchanger.
By heating intake air with exhaust heat and then transferring some of the heat to a powertrain fluid such as engine oil, the fluid may be heated thereby reducing energy losses due to the viscosity of the fluid in addition to reducing combustion chamber heat loss. Further, the heated intake air may be cooled via the heat exchange with the powertrain fluid, yet still be warmer than ambient air such that engine pumping losses may also be reduced, but not so hot that combustion stability is reduced or knock instigated. Further, during warmed-up or boosted operating conditions, for example, heated intake air may cause knock under some conditions; however, during a cold start with the engine warming up, the possibility of the heated intake air causing knock is decreased. As such, a synergistic operation may be achieved.
Another advantage of the disclosed approach is the warming of the engine coolant with air that has picked up heat from the exhaust can increase the heat available for cabin warming. Further, engines often have oil coolers to mitigate peak oil temperatures for engine used at extreme conditions. Thus, the disclosed approach uses the air-to-oil (e.g., gas-to-liquid) heat exchange to achieve oil cooling by reversing the airflow direction via the increased boost, which occurs precisely at times when engine oil cooling needs arise.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.